POTSDAM, Germany-- Cleaning air in Beijing and in other large cities suffering from pollution problems by limiting car and power-plant emissions may raise global temperatures instead of lowering them, a German scientist warns.

Aerosols, or particles suspended in air, have a cooling effect on the Earth, countering global warming linked to carbon dioxide, said Hans-Joachim Schellnhuber, director of the Potsdam Institute for Climate Research.

A drop in aerosols in the atmosphere could cause a "rapid" rise in temperatures, he said.

Airborne pollutants act as an umbrella worldwide while CO2 provides insulation, trapping heat attempting to escape into the atmosphere. A rise in temperature because of declines in aerosols in the atmosphere can be offset by slashing CO2 emissions, he said. By not reducing carbon output, humanity "is closing the last door we have through which we can possibly influence the global climate," Schellnhuber said.